1. Field of the Invention:
This invention relates to a hair treatment composition and more particularly to a hair treatment composition comprising cysteine or a salt thereof, which is capable of preventing flaking of the hair (recrystallization of the composition onto the hair fibres) and is mild to the skin.
2. Description of the Background
Cysteine and its salts possess mild reductivity and are widely used as a component of permanent wave agents, styling agents and so on.
Because of the weak reductivity of cysteine compared to thioglycolic acid, a permanent wave agent containing cysteine is generally used in such manner that the hair is first pretreated with the agent and then wound on a rod by fingers. This means that professional hair dressers' fingers undergo prolonged time of contact with the agent, which causes irritation to the skin of the fingers.
Cysteine is known to have weak reductivity. In order to supplement this weak reductivity, heat is often applied to the hair after treated with a permanent wave first agent containing cysteine. However, it sometimes causes irritation to the scalp.
It has also been noted that cystine, which is formed by oxidation of cysteine, is sparingly soluble and causes "flaking" which is a phenomenon where white crystals are deposited on the hair or on the skin of the fingers. Flaking should desirably be avoided because it brings about unattractive appearance, is rough and imparts a frictional feeling to the touch of the hair and chapped hands or fingers of professional hairdressers.
In order to overcome the flaking, several methods have been proposed, which include a method where a cysteine having racemic structure is used (Jpn. Kokai SHO 56-139411) and a method where N-acyl-cysteine or N-acyl-cystine is used (Jpn. Kokai SHO 52-128241 and 53-72835). These methods, however, result in insufficient waving, or waves, formed by these methods, lack elasticity when compared to those formed by the use of cysteine itself. Another method employs alkanediol added to cysteine (Jpn. Kokai HEI 2-502539). This method is accompanied by the drawback in that a sufficient effect can only be obtained when 300% or more of alkanediol based on cysteine is used, which leads to a restricted formulation of a composition.
Accordingly, development of a hair treatment composition which causes no flaking, is mild to the skin with the inherent activity of cysteine being maintained is still desired.